Transmission of malaria from one human to another is solely dependent upon the successful sporogonic development of the parasite in vector mosquitoes. If a mosquito does not allow the development, the parasite dies and the transmission of malaria is blocked. Interference with parasite development in vector mosquitoes is, therefore, a proposed strategy to block the spread of malaria. To design such strategies, however, an understanding of the parasite development in vector mosquitoes is essential. Development of the malaria parasite in the mosquito is complex. After being ingested by a susceptible mosquito, the parasite undergoes elaborate changes. Expression of stage-specific parasite genes, and interaction of the parasite with various tissues and molecules in the mosquito, accompany these morphologic changes. The development in the mosquito, therefore, is a challenge to the parasite. In fact, most ingested parasites fail to develop successfully, even in a most successful vector. Interruption of the natural course of development in the mosquito would block malaria transmission.In the mosquito, most of the developmental changes occur to parasites while they are associated with the midgut. The majority of parasites die in the midgut. It can be hypothesized that molecules involved with the parasite/mosquito midgut interaction would be crucial determinants of the sporogonic development of the parasite. Therefore it is important to investigate the ookinete interaction with the midgut epithelium and the survival of the parasite in the vector. The information obtained through these studies may lead to development of novel strategies to control malaria. - Mosquito, malaria, vector, disease, transmission, transmission-blocking, parasite